1. Field of the Invention
The present invention relates generally to particle fuel burning furnaces and, more particularly, is concerned with an air inlet valve subassembly which can be installed on new furnaces or retrofitted onto existing furnaces and has a replaceable seal which eliminates the possibility of extended downtime of the furnace for seal repair.
2. Description of the Prior Art
In times of constantly increasing energy costs, the utilization of waste materials as fuel to produce energy is of increasing importance. Waste materials are amply available from various sources, for example, agricultural, forestry and industrial operations.
Many different furnaces (including incinerators and the like) appear in the prior art for burning conventional types of fuel, such as coal and wood, as well as waste or by-product types of particle fuel, such as sawdust, pulverized trash and wood chips. Representative of the prior art are the furnaces disclosed in U.S. Pat. Nos. to Barnett (2,058,945), Evans (3,295,083), Midkiff (3,822,657), Kolze et al (3,865,053; 4,311,102; 4,377,115), Culpepper, Jr. (3,932,137), Leggett et al (3,951,082), Probsteder (4,218,980), Payne et al (4,378,208), Voss (4,385,567) and Ekenberg (4,430,949).
Another prior art furnace for burning waste product particle fuel is manufactured by Eshland Enterprises, Inc. of Greencastle, Pa. under the trademark "Wood Gun". Generally referred to as a wood gasification boiler, it has an insulated housing in which an upper, primary particle fuel retention and combustion chamber and a lower, secondary or afterburning combustion chamber are formed by refractory materials. A series of generally vertically extending passageways interconnect the bottom of the upper chamber with the top of the lower chamber. A quantity of waste particle fuel delivered into the upper chamber of the boiler through a fuel inlet in the top of the housing falls toward the bottom of the upper chamber and forms into a pile of fuel particles. The pile of particle fuel is ignited and burns from the bottom adjacent the location of the passageways. Periodically, the pile is replenished by delivery of additional particle fuel through the top fuel inlet of the housing.
Combustible gases generated as by-products from the burning of the particle fuel in the upper, primary chamber, along with air introduced into the upper portion of the primary chamber above the pile of fuel, are drawn downward through the passageways into the lower, secondary chamber by a draft inducing fan which creates a negative pressure drop in the lower chamber relative to the upper chamber. A suitable heat recovery unit is connected to the lower combustion chamber for capturing much of the heat produced by burning the combustible gases therein.
Air intake valves are mounted through the insulated housing of the furnace and are thermostatically controlled in a known manner to open when the temperature within the furnace falls below a preset level. The fan which induces the downward flow of air in the furnace causes inflow of air into the upper chamber through the valves when they are actuated to their open conditions. When the valves are closed, the upper chamber is substantially sealed. Optimum performance of this type of furnace can only be achieved if the air flow can be stopped completely to thereby prevent combustion from occurring when heat is not required. If a completely air tight seal is not obtained, a low level, smoldering fire will result which produces an overheat situation and undesirable creosote and moisture condensation in the boiler and fuel pile.
Prior attempts to provide a seal which would last through the entire heating season have failed. The presence of creosote and moisture condensation at the valve contact surface causes deterioration of the gasket or seal material. Thus, replacement of the seal at least once, and more likely several times, during the season has usually been necessary.
Heretofore, the gasket seal has been applied in the form of a bead of semi-fluid material about the rim of the air intake spout. Application of the seal occurred as the last step in the manufacture of the furnace in order to minimize the possibility of damage. Also, the rim of the air intake spout and the surface of the valve flap associated with the particular intake spout had to be matched to prevent leakage of air. This proved to be a costly and difficult adjustment to make during manufacture of the furnace. Then, later when gasket failure occurs during use of the furnace as it inevitably does, the problem must be corrected immediately to maintain system efficiency. However, the material best suited for the gasket is high temperature silicone which typically must be air dried for 24 hours before being subjected to operational service. This requirement represents a considerable inconvenience in cold weather when disruption of the heating system for even a few hours may cause severe consequences.
Many different sealable valve constructions used in a variety of different applications are known in the prior art. Representative of the prior art are the devices disclosed in U.S. Pat. Nos. to Crabtree (908,961), Woock (1,341,870), Kilgore et al (1,430,818), Brown (2,277,295), Langdon (2,336,486), Stevens (3,036,814), Conley (3,060,961), Spencer (3,182,951), Merdinyan (3,331,391) and Hansen (3,366,137). While these devices may operate satisfactorily under the particular conditions for which they are intended, it is not seen that any of these devices offer a satisfactory solution to the problem of providing an air tight seal under the rather rigorous environment present in a furnace of the above-described type. Consequently, a need exists for a gasket construction and mounting arrangement which will serve as an effective seal and then, upon failure thereof, can be easily and quickly replaced so as to eliminate the possibility of extended downtime of the furnace.